1. Field of the Invention
The present invention relates to an exposure apparatus used for lithography in manufacturing a semiconductor device, a positioning apparatus suitably used for positioning in various precision machine tools or precision measurement devices, and an exposure apparatus or device manufacturing method using this positioning apparatus.
2. Description of the Related Art
Conventionally, as an exposure apparatus used in manufacturing a semiconductor device, a so-called stepper is known. The stepper projects a reduced image of a pattern formed on a reticle onto a semiconductor wafer through a projecting lens and sequentially exposes the pattern to a plurality of positions on the wafer while moving the wafer stepwise under the projecting lens. The stepper is regarded as a mainstream exposure apparatus because of its performance in resolution and overlay accuracy.
FIG. 24 is a front view showing the main body structure and wafer stage arrangement example of a conventional exposure apparatus.
In FIG. 24, reference numeral 1 denotes an illumination unit for illuminating a reticle pattern; 2, a reticle having a pattern to be transferred; 3, a projecting lens for projecting the pattern formed on the reticle 2 onto a wafer; 4, a lens-barrel holder supporting the projecting lens; 5, a top stage movable in the .theta., Z, .alpha., and .beta. directions, on which a wafer (not shown) is to be mounted; 6, an X-Y stage movable in the X and Y directions, on which the top stage 5 is mounted; 8, a stage base having a guide surface on its upper surface and supporting the X-Y stage 6 and a movable guide 7 in a non-contact state in the Z direction through static pressure air bearing portions; 9, a platform integrated with the lens-barrel holder 4, on which the stage base 8 is mounted and stationarily supported; and 11, air mounts arranged at four positions to support the lens-barrel holder 4. The lens-barrel holder 4 is supported by the air mounts 11 through the platform 9. Reference numeral 33a denotes a laser interferometer for measuring the relative positions of the projecting lens 3 and the X-Y stage 6; 16a, a light-projecting portion of a focus detection unit for measuring the distance between the focal position of the projecting lens 3 and the upper surface of the wafer; and 16b, a light-receiving portion of the focus detection unit.
For the purpose of increasing the area of a semiconductor device and reducing cost, the exposure apparatus having the above arrangement tends to use a large-diameter/size semiconductor wafer. In addition, along with an increase in integration density of a semiconductor device, a strong demand for high-speed and high-precision wafer stage positioning and a high throughput has arisen.
However, to rapidly and precisely move the X-Y stage 6 in such a conventional exposure apparatus to cope with a large-diameter semiconductor wafer to be mounted, the dynamic characteristics of the X-Y stage 6 must be improved. This requires a higher guide rigidity, so the increase in stage weight is inevitably more than the increase in weight due to stroke up. When the moving acceleration and moving speed of the X-Y stage 6 are increased to shorten the moving time to obtain a high throughput, the exciting force generated by the stage moving acceleration becomes larger. In addition to the relative decrease in rigidity of the structure such as the lens holder due to the increase in weight of the projecting lens 3, the prior art has the following problems.
A stronger structure results in a bulky apparatus and an increase in cost.
As the exciting force increases, the characteristic vibration of the entire apparatus supported by the anti-vibration mounts 11 or the mechanical system incorporated in the apparatus is excited. Disturbance vibration is transmitted to the top stage 5 or the laser interferometer 33a, so rapid and precise positioning is impeded.
When the X-Y stage 6 moves, the center of gravity of the entire apparatus which is supported by the lens-barrel holder 4 and the platform 9 changes in the X and Y directions due to the weight of the stage itself, so the distribution of supporting forces of the plurality of air mounts 11 changes. Such a change in supporting force balance deforms the lens-barrel holder 4 which serves as the reference of the focus sensors 16a and 16b and the laser interferometer 33a for measuring the position and posture of the X-Y stage 6, thus degrading the overlay accuracy of a wafer or the like.
In a positioning apparatus disclosed in, e.g., U.S. Pat. No. 5,610,686 or Japanese Laid-Open No. 7-335538, a linear motor applies an acceleration to the stage in correspondence with vibration of the base to prevent a relative shift between the base and the stage due to vibration of the base upon driving the stage on the base.
However, when the stage moves, the center of gravity of the entire apparatus changes in the X and Y directions due to the weight of the stage itself, so the distribution of supporting forces of a plurality of holders supporting the entire positioning apparatus changes. Such a change in supporting force balance deforms a holder which serves as the reference of the focus sensors and the laser interferometer for measuring the position and posture of the X-Y stage, thus degrading the overlay accuracy of wafer or the like.
In the above prior art described in Japanese Laid-open No. 7-335538, an acceleration is given by a linear motor to cancel the driving reaction force of the stage which is driven by a ball screw. However, when two actuators (the ball screw and linear motor) are attached to one stator or table, the acceleration is not satisfactorily transmitted, so this system can hardly be realized. Because the actuator (linear motor) is different from the driver of the stage (ball screw), it is very difficult to properly cancel a small vibration generated by a driving reaction force of the stage.
In a positioning apparatus disclosed in Japanese Patent Laid-Open No. 3-21894, 3-107639, or 3-125048, a balance member is driven by a ball screw to apply an acceleration corresponding to vibration to the base or stage in order to prevent vibration of the base or stage.
However, since the ball screw is used to move the stage or balance member, a moment is generated around the shaft of the ball screw. The rotational moment may act on the base or stage to generate disturbance vibration, resulting in a decrease in stage positioning accuracy. In addition, a lubricant or the like is required for use of a ball screw, so the stage cleanness or maintenance properties become lower.
Furthermore, a system using a ball screw subjected to mechanical contact cannot completely suppress characteristic vibration, so residual vibration is generated. Therefore, a more advanced control system must be constructed for the balance member.
In recent years, the line width of the integration circuit of a semiconductor wafer has been reduced to the submicron order. Excitation of such vibration by a ball screw largely adversely affects the performance of an exposure apparatus.